flyhigh@mach1

Hello all,

I've had my FRPP dual exhaust kit on my 2006 V6 for 6 months now. It sounds great. My engine has the well known 800 RPM & 1800 RPM resonance/vibration that V6's produce. I have modified the transmission mount rubber hangers with heavy duty mounts and it took care of most of the vibration I was getting while idling in drive with the A/C on. All exhaust hangers and heat shield clearances have been checked...all good! But I still have the resonance drone at those RPM's. Ford used vibration/counter weights that attached to the stock single mid-exhaust pipe and the stock muffler to deal with the inherent vibration problem. I've attach a pic of the weights. Has anyone saved and re-attached these stock anti-vibration weights to their new dual exhaust systems? What causes the resonance....is it from the engine internals? Thanks all!



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flyhigh@mach1

Also, here is the transmission mount modification I performed. I bought a much thicker rubber mount from NAPA and installed it with large hose clamp...similar to what Ford wanted dealers to do to deal with the vibration. Works very well and even though Ford claims they are not needed, it really helps to stabilize the whole exhaust system. When I cut the stock hangers off, the exhaust system really vibrated at idle with A/C running. Worked for me and easy fix!

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astentine

I'll try to keep my response quick and too the point. I'm an aerospace engineer dealing with structures and actually just did a project on "why the hell are my mufflers so damn loud at 2250 RPM".

I'm going to assume since you're talking about resonance you're getting either rattling (caused by the excessive movement that is amplified by driving at the exhaust's resonance frequency) or just a loud tone at specific RPMs.

Well, it turns out you can convert an engine's RPM into a usable frequency in hertz. Google search it, I can't remember what it is. Anyway, resonance is more or less an inherent property of the system. Adding weights (mass) will drop the resonance (simplistically of course). In my case, the muffler's had a large resonance amplitude right at the frequency that corresponds to 2250 RPM.

Most of the noise and vibration will come from the properties of the system alone. You can add weights (mostly to the mufflers as they are what is actually producing the resonance, they all, after all, just one big resonator), but that could also create different moments and torques and may even worsen the problem if they are allowed to bang off the rest of the car.

Bottom line, engine internals pushes the gas through the system at a cyclic rate, which is turned into a frequency. The mufflers have their own resonance. If the engine's output frequency matches the muffler's system frequency, you will get a loud response (and even large vibrations). Only way to change it is to change the muffler.

I hope this kind of helps out.

flyhigh@mach1

This vibration or resonance is typical of this engine. I have read many threads complaining about the specific RPM points I stated. Ford engineers obviously know about it as well due to adding weights to the stock single exhaust system. So you believe it is a pressure issue and not an internal balance issue of the 4.0 V6 engine. I believe that since the weights are/were located on the pipe and the muffler. So has anyone added back the stock weights to your new dual exhaust system? I'm thinking about visiting a few muffler shops and asking them if they have any in the scrap pile. Worth trying IMO.

astentine

Yeah, definitely internal pressure and no balance issues. Sure, give the weights a try if you can pick up some cheap, why not. It may change the system properties enough to drop the resonances out of the trouble range.

Boneman

Not had any issues with the exhaust resonance... and I have pypes X-pipe on mine with GT exhaust components from there back. Now my CLUTCH on the other hand.... I had the "helicopter" clutch issue as described in this TSB:

http://www.stangpit.com/wp-content/i...b/08-08-05.pdf

They purported that it would not effect longevity, etc., but the T.O. bearing failed at 135K miles.... perhaps that's expected... but maybe not. As it were, you can see that the fix for this simple harmonic resonance issue was extensive and expensive, so I blew it off. Since recently replacing the clutch, T.O. Bearing / slave cyl. and having of course had the flywheel turned.... that issue is GONE.

So a re-design of the clutch and flywheel took care of that. As to exhaust, yeah, a little tweeking may do you a world of good. BTW... one of the "vibration" issues... the TSB that is referenced in the TSB linked... is to REMOVE the exhaust mounting brackets at the trans crossmemeber.... They did that to mine before determining that I had the helicopter clutch issue.

You may want to try that.... take your extra heavy duty rubber mounts off entirely.... just to see.

Good luck! I know how frustrating this sort of thing can be... after all, I lived with a helicopter clutch for 65K miles. Helps to have 650 watts of stereo to ... "mitigate" the issue.

flyhigh@mach1

Thanks for the responses. I went by the performance shop that installed my exhaust, and they have never had anyone want the weights re-installed. It's not bad really, just noticeable enough to wonder why it does what it does at those specific RPM's. Also, I did remove the transmission exhaust mounts...I had excessive idle vibration of the exhaust pipes. Heavy duty rubber mounts solved that problem.

mcrider

I had the exact same problem when I put duals on my 2007 V6 mustang. All I had to do to completely stop the droning resonance is move the mufflers from behind the axle to directly under the car between the front and back seats, Period, no more droning!!! I didn't like the sound of the mufflers I had on my car, so I did replace them with 24" glass pacs and they sound awesome! The only thing I can think of is that with the mufflers behind the axle, the droning noise comes up through the trunk area into the cabin. With the mufflers under the cabin, there is no droning sound at all in the car. All I hear is the sweet music of the exhaust

flyhigh@mach1

That's interesting that moving mufflers forward stopped the drone. Maybe the closer to the engine, reducing distance or "arm", is enough to change vibration. I'm not going to move my mufflers, and I don't have drone. It's a distinct vibration passing thru 800 rpm's and 1700 rpm's. If I stay right at 1700 rpm's, it can get annoying. And with A/C on, then 800 RPM's can vibrate the car. I was told by a mechanic that V6's are not well internally balanced engines, and that's the cause of the vibration. What do you guys think?

mcrider

The only Vibration I have in my V6 is at idle and it is not bothersome. None anywhere else in the powerband. My Mustang is an '07 that was given to me as a birthday present. It was 2 years old and had a blown engine as the result of a 19 year old hot rodding it to oblivion. I replaced the engine with a V6 that came out of an '06 mustang with 24,000 miles on it, so it is the same V6 that you have. I can't imagine what is causing your vibration, as mine has none. Like I said, It did have a terrible droning resonance, so bad that I couldn't stand to drive it for more than 30 minutes. I finally "reasoned" that it must be the frequency of the resonance or vibrations as they came through the mufflers and that since they were directly under the trunk, that maybe the trunk area was amplifying them like the inside of a steel drum. That is why I moved them directly under the cabin area and it worked better than I could have ever expected. I am so happy with my 'Stang now. I love it!